Watermarking is the process of embedding information into a given object or signal, such as, for example, an image or a video signal, preferably in such a manner that the embedded information is imperceptibly added to the given signal. That is, although the resultant signal appears to the casual viewer as being unmodified (as compared to the original signal), it in fact contains embedded information which can be recovered if and when desired.
Generally, video and image digital watermarking technologies fall into two categories. The most common form of digital watermarking is known as indelible marking, in which a typical user cannot remove the watermark. This form of watermarking is often used, for example, to provide copyright protection for proprietary videos or images. The second form of digital watermarking is known as recoverable watermarking. Recoverable watermarking is a method of embedding information in an image or video signal, usually with the goal of recording some useful information to accompany the image or the video. With recoverable watermarking techniques, a user would be able to defeat (e.g., remove) the watermark, but would presumably want the information and would not do so. This type of watermarking may be used to embed useful additional data into the signal, such as, for example, information about a product being advertised in a video commercial. For example, when such a commercial airs, the version of the commercial and specific products (such as, for example, sale items at a grocery store) can be easily recovered.
Another example of useful data to be embedded (i.e., watermarked) into a video signal with the use of a recoverable watermark might be the date and time that each video frame (i.e., individual video image) of the recording was captured, possibly as well as information which identifies the particular recording device (i.e., a camera) which was used. In this manner, each frame of the resultant video can be uniquely identified by a decoder of the video signal. And since a given recording device only records one video at a time, this approach results in a unique identification of each frame recorded in any number of videos. Similarly, for an image (e.g., a digital photograph), it may be desirable to watermark the image with the date and time that the image was captured (e.g., when the photograph was taken), which may be used for archival purposes.
One limitation with current methodologies for performing video (as well as image) watermarking is that they do not survive typical video (or image) compression techniques—that is, the compression process destroys the watermark. For example, since most video signals are compressed with use of a video compression algorithm such as, for example, MPEG-2, MPEG-4, H.263 or H.264, this puts severe constraints on who can add the watermark, and where in the video transmission network such watermarking can be done. (MPEG-2, MPEG-4, H.263 and H.264 are all video compression standards, each of which is fully familiar to those of ordinary skill in the art.) And technologies that require compression to the home, such as, for example, satellite TV or video-over-DSL, cannot, therefore, use the current technology.